Magnetic field generation device with alternative quench device

ABSTRACT

A magnetic field generation device for a magnetic resonance tomography apparatus has a vacuum container that encloses a magnetic coil made of superconducting material, and a conduit of a pipe system is connected with the magnetic coil so as to conduct heat. The pipe system and the conduit are filled with a coolant that places the magnetic coil in a superconducting state during normal operation of the tomography system. A valve connects the pipe system to the interior of a capture container. In the event of non-normal operation, such as a quench, evaporated coolant passes through the valve into the capture container.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a magnetic field generation device for anapparatus for magnetic resonance tomography, as well as an apparatus formagnetic resonance tomography with such a magnetic field generationdevice.

2. Description of the Prior Art

Magnetic resonance tomography is an imaging modality for which very highmagnetic fields (up to multiple Tesla) are required. Superconductingmagnetic coils are used to generate such high magnetic fields. So thatthe material of the magnetic coils is superconducting, it must besignificantly cooled. Such a cooling typically takes place with liquidhelium. The helium in conventional apparatuses for magnetic resonancetomography is located together with the magnetic coils in a cryostat.The container in which the liquid helium and the magnetic coils arelocated is surrounded by a thermally insulated vacuum container with avacuum therein. If the magnetic coils transition into the normallyconductive state, an event known as a quench occurs, and the energy ofthe magnetic field is transduced into heat. The liquid helium therebysuddenly vaporizes and expands at the transition into the gas phase. Inorder to avoid an explosion of the cryostat, the gas is discharged via acomponent known as a quench pipe. In order to avoid consequential damage(such as asphyxiation of patients and treatment personnel), the gaseoushelium is discharged into a region outside of the room in which theapparatus for magnetic resonance tomography is located. The helium isthereby lost, and an expensive refilling of the cryostat with liquidhelium is necessary. Furthermore, the installation of a quench pipe iscomplicated, and the quench pipe, or the valve installed therein, mustbe regularly monitored for blockage (for example by ice formation).

From DE 10 2005 042 112 B3, a device is known for monitoring a quenchpipe of a superconducting magnet with a quench pipe inside of which arearranged at least one illumination unit and at least one imageacquisition unit. The image acquisition unit is furthermore connectedwith an image presentation unit so that the state of the inside of thequench pipe can be monitored visually. Blockages (by ice, for example)can therefore be detected.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetic fieldgeneration device with an alternative quench device that allows arecovery of the coolant evaporated upon a quench.

The invention is based on a magnetic field generation device, wherein avacuum container surrounds at least one magnetic coil made ofsuperconducting material, and a conduit connected with the coolantcirculation system is connected with the superconducting magnetic coilso as to conduct heat, at least in part. When the circulation system(and therefore the conduit) is filled with a coolant, the conduit coolsthe magnetic coil. The invention is based on connecting a valve with thecirculation system so that the valve is suitable to regulate the passageof gases between the circulation system and the inside of a capturecontainer. In the event of a quench, the evaporated coolant cantherefore be captured in the capture container and be recovered again.

In a further embodiment, the capture container to capture the coolant isthe vacuum container, so the valve between the conduit and the inside ofthe capture container is not at risk of icing over, since the moisturein the vacuum container is extremely low.

In a further embodiment, the pipe system has at least one conduit thatproceeds along the winding of the magnetic coil. A particularlyefficient cooling is thereby enabled.

In a further embodiment, a pressure sensor is arranged in the pipesystem and/or one of the aforementioned valves is equipped with apressure sensor so that the pressure inside the pipe system can bemonitored.

In a further embodiment, the magnetic field generation device has anadditional valve that is suitable for regulation of the passage of gasesbetween the inside of the capture container and the space outside ofsaid capture container. The coolant can thereby be particularly simplyrecovered from the capture container after a quench.

In a further embodiment, at least one conduit of the pipe system can beconnected with a reservoir so that an outlet exists for gases and/orfluids from the reservoir into the pipe system. If the pipe system isfilled with fluid, cooling is thereby enabled via the thermosiphonprinciple.

The invention also encompasses an apparatus for magnetic resonancetomography with a magnetic field generation device according to any ofthe above-described embodiments, wherein the valve is mounted above themagnetic coil, between the pipe system and the inside of the vacuumcontainer. The apparatus enabling the gaseous coolant to escape in theevent of a quench, with no liquid coolant coming into contact with thevalve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a magnetic field generation device inaccordance with the invention in cross-section, for a magnetic resonancetomography apparatus.

FIG. 2 shows a further embodiment of a magnetic field generation devicein accordance with the invention in cross-section, for a magneticresonance tomography apparatus.

FIG. 3 shows a magnetic resonance tomography apparatus in accordancewith the invention, in longitudinal section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a magnetic field generation device for a magnetic resonancetomography apparatus, having a cylindrical vacuum container 6 in whichare located multiple annular magnetic coils 1 made of superconductingmaterial. The vacuum container 6 and the magnetic coils 1 are arrangedessentially concentrically. Furthermore, the magnetic field generationdevice has a pipe system 7 that has conduits 2 that have aheat-conducting connection with the magnetic coils 1 and are in partarranged concentrically with the magnetic coils 1. The pipe system 7 isfilled with liquid helium 3 as a coolant. Liquid helium 3 enables thesuperconducting material of the magnetic coil 1 to be cooled below thetransition temperature, such that it transitions from the normallyconducting state into the superconducting state. The filling of the pipesystem 7 requires markedly less liquid helium 3 than submerging themagnetic coil 1 into liquid helium 3, as in conventional cryostats. Forthe magnetic field generation device shown here, only approximately 0.02m³ liquid helium 3 is required for the magnetic resonance tomographyapparatus (in particular for medical imaging).

Furthermore, a first valve 5 is mounted at a conduit 2 of the pipesystem 7 so that it enables gaseous helium 4 to pass from the pipesystem 7 into the vacuum container 6. In the event of a quench, thegaseous helium 4 can then be conducted into the vacuum container 6. Thegaseous helium 4 cools due to the expansion in the vacuum container 6.Due to the reduced volume of the liquid helium 2 relative toconventional cryostats, the gaseous helium 4 can be captured by thevacuum container 6 without danger.

The magnetic field generation device has a second valve 10 that issuitable to regulate the passage of gases (in particular of gaseoushelium 4) between the inside of the vacuum container 6 and the spaceoutside of the vacuum container 6. It is thereby possible to capture thegaseous helium 6 and reuse it.

The magnetic field generation device has a third valve 11 that issuitable to regulate the passage of gases (in particular of gaseoushelium 4) between the pipe system 7 and the space outside of the vacuumcontainer 6. For example, in the event of a quench the gaseous helium 4can first be diverted into the vacuum container 6 until a certainpressure has built up in it. The remaining gaseous helium 4 (which is ata lower pressure than the gas escaping at the start of the quench) canthen be harmlessly diverted into a space, for example into the room inwhich the magnetic resonance tomography apparatus is located, or eveninto the open environment with the use of a quench pipe. If a quenchpipe is used, it turns is markedly smaller than in prior art systems,because less gas, under lower pressure, must be diverted. In particular,the quench pipe can have a diameter of less than 10 cm.

A pressure sensor 12 is arranged in the pipe system 7 so that thepressure inside the pipe system 7 can be measured. Furthermore, thefirst valve 5 between the pipe system 7 and the inside of the vacuumcontainer 6 and/or the third valve 11 between the pipe system 7 and thespace outside of the vacuum container 6 can be opened or closeddepending on the pressure measured by the pressure sensor 12. Inaddition or as an alternative to the pressure sensor 12, the first valve5 between the pipe system 7 and the inside of the vacuum container 6and/or the third valve 11 between the pipe system 7 and the spaceoutside of the vacuum container 6 can have a pressure sensor 5.

The conduit 2 is formed of aluminum, but other, non-ferromagneticmaterials can also be used to produce the conduit 2. The individualconduits 2 are connected with one another by welding seams, but otherjoining techniques (such as gluing, riveting or bolting) can be used.

Furthermore, the pipe system 7 is connected with a cryo-unit 8 so thatgaseous helium 4 is conducted through the pipe unit [sic] 7 to thecryo-unit 8. For this, a conduit 2 connects the upper part of the pipesystem 7 with the upper part of the cryo-unit 8. The cryo-unit 8comprises a reservoir 13 and a cooling head 8 that is located in thereservoir 13. A circulation of the coolant according to the thermosiphonprinciple can be realized simply with the aid of the cryo-unit 8. Thecooling head 8 cools the evaporated gaseous helium 4 until it condensesin the reservoir 13 and, as liquid helium 3, is available again ascoolant. For this, a conduit 2 connects the lower part of the pipesystem 7 with the lower part of the cryo-unit 8. The cryo-unit 8 canalso be located within the vacuum container 6 or in a separate cryostat,which is different than is shown in FIG. 1.

FIG. 2 shows a magnetic field generation device for an apparatus fornuclear magnetic resonance tomography, comprising a cylindrical vacuumcontainer 6 in which are located likewise cylindrical magnet coils 1made of superconducting material. The vacuum container 6 and themagnetic coil 1 are arranged essentially concentrically. Furthermore,the magnetic field generation device has a pipe system 7 that hasconduits 2 that have a heat-conducting connection with the magneticcoils 1 and are arranged concentrically in part with the magnetic coils1. The pipe system 7 is filled with liquid helium 3. The gaseous helium4 collects in the upper part of the pipe system 7. In the event of aquench, the helium 4 can be diverted through the valve 5 (which isprovided with a pressure sensor 12) into a capture reservoir 15 that islocated next to the magnetic resonance tomography apparatus, andtherefore outside of the vacuum container 6. This capture container 15can be designed to withstand its high pressure and compress the incominggaseous helium 4. Analogous to the description in FIG. 1, such a capturecontainer 15 can be equipped with a second valve 10 to recover thegaseous helium 4.

FIG. 3 shows a magnetic resonance tomography apparatus in longitudinalsection with annular magnetic coils 1 that are located in a cylindricalvacuum container 6, wherein the magnetic coils 1 and the vacuumcontainer 6 are arranged essentially concentrically. The pipe system 7is likewise located in the vacuum container 6 and has conduits 2 thatare in heat-conducting contact with the magnetic coils 1. Conduits 2thereby extend like a fan between the annular magnetic coils 1.Furthermore, the pipe system has two cylindrical conduits 2, wherein onecylindrical conduit 2 is located on the inner side facing towards thepatient 17 and the other conduit 2 is located on the outer side facingaway from the patient 17. The two cylindrical conduits 2 are connectedwith one another via the fan-like conduits 2 between the coils so thatthey form a common internal space for circulation of the liquid helium3.

Furthermore, the pipe system 7 has two valves 5 with a respectivepressure sensor 12 that are suitable to conduct gaseous helium 4 intothe inside of the vacuum container 6 in the event of a quench. Thevacuum container 6 has an additional valve 10 that is suitable toconduct gaseous helium 4 out of the vacuum container 6 into thesurrounding space. The valve 10 can be used in order to recover thegaseous helium 4 after a quench.

Furthermore, the pipe system 7 has a conduit 2 that extends into thespace outside of the vacuum container 6. This conduit 2 furthermore hasa burst disc 14 so that the gaseous helium 4 can also be conducted intoa space outside of the vacuum container 6 in the event of a quench andtoo high a pressure in the pipe system 7. With the burst disc 14 theconduit 2 can be connected with a quench pipe in order to be able toconduct the gaseous helium 4 into the free environment.

The magnetic resonance tomography apparatus also has radio-frequencycoils 19 that are suitable for transmission and/or reception ofradio-frequency signals. They are located outside of the vacuumcontainer 6 on the side facing toward the patient 17. Theradio-frequency coils 19 and the vacuum container 6 are both surroundedby a cylindrical casing 18. The tube formed by the casing 18 is suitableto position the patient 17 on a patient bed 16 in the tube so that hecan be examined with the nuclear magnetic resonance tomographyapparatus.

However, the conduits 2 can also be situated inside the body of themagnetic coil 1 or run through said magnetic coil 1, which is differentthan in Figures described here. Moreover, the conduit 2 can also befashioned as channels in an aluminum tube that is multiple centimetersthick.

Deviating from the structure specifically shown in the drawings, themagnetic coils 1, the radio-frequency coil 19 and also the conduit 1 inheat-conducting contact with the magnet coils 1 need not be shapedannularly, but rather as polygons and/or cylindrically shaped or evenasymmetrical bodies, for example.

Although liquid helium 3 is presently necessary as a coolant in order tocool superconducting materials (that are suitable for constructingmagnetic coils 1) below the transition temperature, it is not precludedthat other coolants will be used in apparatuses for magnetic resonancetomography in the future. Therefore, the embodiments of this inventionare not limited to the use of liquid helium 3 as a coolant.

Although modifications and changes may be suggested by those skilled inthe art, it is the intention of the inventor to embody within the patentwarranted hereon all changes and modifications as reasonably andproperly come within the scope of his contribution to the art.

I claim as my invention:
 1. A magnetic field generation device for amagnetic resonance tomography apparatus, said magnetic field generationdevice comprising: a vacuum container that generates a vacuum inside ofthe vacuum container; at least one magnetic coil made of superconductingmaterial that is enclosed by said vacuum container; a pipe systemcomprising at least one conduit in heat-transferring communication withsaid magnetic coil, said conduit containing a liquid coolant thereinthat places said superconducting material in a superconducting stateduring a normal operating condition of said magnetic resonancetomography apparatus, and at least a portion of said liquid coolanttransitioning to a gas in a non-normal operating state of said magneticresonance tomography apparatus; a capture container; and a valveconnected with said pipe system that regulates passage of said gasbetween said pipe system and an interior of said capture container.
 2. Amagnetic field generation device as claimed in claim 1 wherein saidcapture container is formed by said vacuum container.
 3. A magneticfield generation device as claimed in claim 1 wherein said magnetic coilis formed in a coil winding, and wherein said at least one conduitproceeds along said coil winding.
 4. A magnetic field generation deviceas claimed in claim 1 comprising a pressure sensor in said pipe systemthat causes said valve to open upon detection of a pressure associatedwith said non-normal operating condition.
 5. A magnetic field generationdevice as claimed in claim 1 wherein said valve comprises a pressuresensor that opens said valve upon sensing of a pressure associated withsaid non-normal operating condition.
 6. A magnetic field generationdevice as claimed in claim 1 wherein said valve is a first valve, andcomprising a second valve that regulates passage of said gas betweensaid interior of said capture container and an ambient space outside ofsaid capture container.
 7. A magnetic field generation device as claimedin claim 1 wherein said conduit is a first conduit, and comprising asecond conduit that places said capture container in a circulating fluidcommunication with a remainder of said pipe system.
 8. A magnetic fieldgeneration device as claimed in claim 1 wherein said capture containeris a reservoir that is connected to said pipe system only by saidconduit, said reservoir having a reservoir outlet allowing said gas toexit said reservoir to an exterior of said reservoir.
 9. A magneticresonance tomography apparatus comprising: a magnetic resonance dataacquisition unit; a vacuum container in said data acquisition unit thatgenerates that generates a vacuum inside of the vacuum container; atleast one magnetic coil that generates a static magnetic field in saiddata acquisition device, said at least one magnetic coil being made ofsuperconducting material that is enclosed by the vacuum container; apipe system comprising at least one conduit in heat-transferringcommunication with said magnetic coil, said conduit containing a liquidcoolant therein that places said superconducting material in asuperconducting state during a normal operating condition of saidmagnetic resonance tomography apparatus, and at least a portion of saidliquid coolant transitioning to a gas in a non-normal operating state ofsaid magnetic resonance tomography apparatus; a capture container; and avalve connected with said pipe system that regulates passage of said gasbetween said pipe system and an interior of said capture container. 10.A magnetic resonance tomography apparatus as claimed in claim 9 whereinsaid capture container is formed by said vacuum container.
 11. Amagnetic resonance tomography apparatus as claimed in claim 9 whereinsaid magnetic coil is formed in a coil winding, and wherein said atleast one conduit proceeds along said coil winding.
 12. A magneticresonance tomography apparatus as claimed in claim 9 comprising apressure sensor in said pipe system that causes said valve to open upondetection of a pressure associated with said non-normal operatingcondition.
 13. A magnetic resonance tomography apparatus as claimed inclaim 9 wherein said valve comprises a pressure sensor that opens saidvalve upon sensing of a pressure associated with said non-normaloperating condition.
 14. A magnetic resonance tomography apparatus asclaimed in claim 9 wherein said valve is a first valve, and comprising asecond valve that regulates passage of said gas between said interior ofsaid capture container and an ambient space outside of said capturecontainer.
 15. A magnetic resonance tomography apparatus as claimed inclaim 9 wherein said conduit is a first conduit, and comprising a secondconduit that places said capture container in a circulating fluidcommunication with a remainder of said pipe system.
 16. A magneticresonance tomography apparatus as claimed in claim 9 wherein saidcapture container is a reservoir that is connected to said pipe systemonly by said conduit, said reservoir having a reservoir outlet allowingsaid gas to exit said reservoir to an exterior of said reservoir.